Faculty Profiles - KATO Junji

Multiscale Topology Optimization Applying FFT-Based Homogenization

Matsui, M; Hoshiba, H; Nishiguchi, K; Ogura, H; Kato, J

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Vol. 126 ( 4 ) 2025.2

Publisher：International Journal for Numerical Methods in Engineering

Advances in 3D-printing technology have enabled the fabrication of periodic microstructures that exhibit characteristic mechanical performances. In response, multiscale topology optimization, which finds the optimal design of microstructure for the macrostructure geometry and performance requirements, has become a hot topic in the field of structural optimization. While the basic optimization framework based on the homogenization theory spanning macro and microscales is available, it is computationally expensive and not easily applicable in practical scenarios such as high-resolution design for precision modeling and reliable design considering non-linearities. To address this issue, we focus on a homogenization analysis using a fast Fourier transform as an alternative approach to conventional finite element analysis and develop an optimization method with fast computing speed and low memory requirements. In this paper, we define a simple stiffness maximization problem with linear elastic materials and conduct two and three-dimensional optimization analyses to evaluate the validity and performance of the proposed method. We discuss the advantages of computational cost, the influence of the filtering process, and the appropriate setting of material contrast.

DOI： 10.1002/nme.70009

TOPOLOGY OPTIMIZATION INCLUDING CONSTRAINTS FOR UNIFORM REACTION FORCES DISTRIBUTION Open Access

LIU Guangwei, HOSHIBA Hiroya, NISHIGUCHI Koji, KATO Junji

Journal of JSCE Vol. 13 ( 2 ) page： n/a 2025

Language：English Publisher：Japan Society of Civil Engineers

The present study proposes a method to maximize the stiﬀness of a structure considering the uniform distribution of reaction forces. The variance of the reaction forces at the Dirichlet boundary is introduced to evaluate the uniformity of the reaction forces. Several formulations for optimal topology design are provided by introducing the constraints of variance of reaction forces. Multi-objective optimization considering mean compliance minimization and uniform distribution of force transmission is proposed by dimensionless quantity description. Sensitivity analysis is then derived based on the adjoint variable method and veriﬁed by the ﬁnite diﬀerentiation approximation(FDA). Several numerical examples verify the eﬀectiveness of the proposed method.

DOI： 10.2208/journalofjsce.24-15005

Design and evaluation of bridge collapse protection brackets using topology optimization techniques Open Access

Kitada Yukio, Kurokawa Takahiro, Yoshii Shotaro, Matsumura Toshio, Matsuoka Tsutomu, Kato Junji

Journal of Structural Engineering, A Vol. 71A ( 0 ) page： 59 - 69 2025

Language：Japanese Publisher：Japan Society of Civil Engineers

A lightweight and highly rigid shape for a bridge collapse protection bracket was developed using topology optimization. The design was refined for compatibility, manufacturability, and cost-effectiveness, resulting in a commercially viable product. This paper aims to verify the final design, demonstrating a balance between weight reduction and performance. A full-scale product was fabricated using a 3D sand mold layering machine based on the final design, and its performance was validated through experimentation. A comparative analysis with computational results also confirmed the performance and safety of the final design.

DOI： 10.11532/structcivil.71a.59

SHAPE DESIGN OF BRIDGE COLLAPSE PROTECTION BRACKET APPLYING TOPOLOGY OPTIMIZATION TECHNIQUES

KITADA Yukio, KUROKAWA Takahiro, MATSUMURA Toshio, KATO Junji

Kou kouzou rombunshuu Vol. 31 ( 123 ) page： 123_69 - 123_80 2024.9

Language：Japanese Publisher：Japanese Society of Steel Construction

A lightweight and exceptionally rigid cast metal configuration has been carrying out technological development through the implementation of a topology optimization technique for a bracket designed for a bridge collapse prevention system. Nonetheless, the configuration derived from rudimentary unitary analysis did not result in optimal performance when subjected to combined analysis replicating the installation state. Consequently, for the purpose of enhancing performance, formulated an optimization method encompassing meticulously devised analytical conditions. The configuration obtained through this method is approximately 30% lighter than the conventional shape, while maintains equivalent or heightened rigidity.

DOI： 10.11273/jssc.31.123_69

Eulerian elastoplastic simulation of vehicle structures by building-cube method on supercomputer Fugaku

Nishiguchi K., Takeuchi S., Sugiyama H., Okazawa S., Katsuhara T., Yonehara K., Kojima S., Kawahara K., Hoshiba H., Kato J.

ACM International Conference Proceeding Series page： 145 - 153 2024.1

Authorship：Last author Language：English Publishing type：Research paper (international conference proceedings) Publisher：ACM International Conference Proceeding Series

This paper presents a novel numerical method for the elastoplastic simulation of vehicle component structures under large deformation problems, such as crash-worthiness analysis. Elastoplastic simulation of vehicle structures is essential for designing safer and more efficient vehicles, but poses significant challenges for a conventional finite element method (FEM) due to the limitation of parallel performance and mesh distortion at large deformations. To overcome these challenges, we propose using the cell-centered finite-volume method (CCFVM) in the Eulerian description and the building-cube method (BCM). The Eulerian CCFVM is a robust scheme for solving large deformations of the continuum by spatially fixed collocated Cartesian mesh, which enables a simpler data structure than conventional FEM. The BCM is a hierarchical Cartesian mesh approach in which the computational domain is divided into cubic regions with adaptive refinement suitable for parallel computing. The combination of Eulerian CCFVM and BCM enables us to perform high-fidelity simulations of vehicle component structures. We demonstrate the validity and scalability of the present method by computing a three-point bending test of vehicle component structures using different geometries, such as impact beams. The numerical results show good agreement with the reference results obtained by LS-DYNA, a commercial FEM code. We also achieve a weak scaling of 73.5% in an elastoplastic simulation of about 540 million cell mesh using 131,072 cores of supercomputer Fugaku. The proposed method is expected to contribute to the development of geometrically complex crushable structures by giga-casting and 3D printing, which are emerging manufacturing techniques for vehicle structures.

DOI： 10.1145/3635035.3635038

Generative model of three-dimensional shapes incorporating structural mechanics

Toida Issei, Nishiguchi Koji, Chiba Naoya, Wada Yuji, Yokota Rio, Hoshiba Hiroya, Kato Junji

Transactions of the Japan Society for Computational Engineering and Science Vol. 2024 ( 1 ) page： 20241010 - 20241010 2024

Language：Japanese Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

We propose a deep generative model for 3D shapes that incorporates structural mechanics parameters, and a dataset of 6667 shapes created by topology optimization. Our model is based on DeepSDF, a decoder-type neural network that implicitly represents shapes as signed distance functions (SDFs). We extend DeepSDF to condition the shape generation on structural mechanics parameters, such as strain energy, load direction, volume, and dimension. We also introduce positional encoding to improve the spatial resolution of the model. Our dataset consists of various 3D shapes computed by a linear topology optimization method using the Building-Cube method. We use the strain energy as a quantitative indicator of the structural performance of the shapes. We train our model on the dataset and evaluate its ability to generate 3D shapes reflecting structural mechanics parameters. Our results indicate that our model can produce 3D shapes with high fidelity and diversity, and achieve an average reconstruction accuracy of 88.8% for the test shapes. Our model and dataset open up new possibilities for 3D shape generation and structural design using deep learning.

DOI： 10.11421/jsces.2024.20241010

Fundamental study on topology optimization using quantum annealing and generalized Benders decomposition

HAGA Shiori, YAMAMOTO Yoshihito, NONOBE Koji, MURAMATSU Mayu, KATO Junji

Artificial Intelligence and Data Science Vol. 5 ( 3 ) page： 719 - 729 2024

Language：Japanese Publisher：Japan Society of Civil Engineers

The goal of this research is to establish a topology optimization method using quantum annealing that can search for a better optimal solution at high speed without falling into a local optimum. As a fundamental step, we have implemented and verified a method for topology optimization of two-dimensional trusses using quantum annealing and generalized Benders decomposition. In particular, the method was verified under conditions that have not been used in previous studies, and the effects of various calculation conditions on the results were evaluated. The verification results show that the proposed method is capable of performing reasonable optimal calculations, and that the penalty coefficient for the volume constraint and the setting of the volume change in the iterative step of the optimal calculation process are particularly important to obtain reasonable calculation results with the proposed method.

DOI： 10.11532/jsceiii.5.3_719

Topology optimization of connectable microstructure using enlarged connective domain Reviewed

Matsui, M; Hoshiba, H; Kamada, H; Ogura, H; Kato, J

STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION Vol. 66 ( 8 ) 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Structural and Multidisciplinary Optimization

Advances in 3D-printing technology have made it possible to manufacture structures containing periodic microstructures (lattice structures) and obtain superior mechanical performance that cannot be provided with uniform solids. To achieve the best performance, microstructures with different properties should be optimally designed and arranged in the right places within the macrostructure. However, in most of the basic approaches with homogenization theory, each microstructure is analyzed and optimized separately under periodic boundaries, so connectivity with adjacent microstructures is not considered (or guaranteed). Consequently, unrealistic discontinuous structures are often obtained, resulting in poor mechanical performance and manufacturability. To address this problem, we propose a method to introduce an "enlarged connective domain" around the boundary when dividing the macrostructure into multiple domains with different microstructures in advance. The microstructure of the enlarged connective domain is formed by combining the unit cells of adjacent microstructures, which allows micro-scale connectivity to be reflected in the macrostructure. Therefore, this method improves the mechanical connectivity between microstructures through the original optimization process of maximizing the performance of the entire macrostructure. This paper demonstrates that the proposed method improves connectivity and mechanical performance by performing optimization analyses for two- and three-dimensional problems. In addition, we focus on the width (volume ratio) of the connective domain as a design parameter that specifies the degree to which connectivity is considered and discuss how to set the parameter appropriately.

DOI： 10.1007/s00158-023-03613-w

Multi-material topology optimization considering strengths of solid materials and interface Reviewed

WATANABE Daiki, HOSHIBA Hiroya, NISHIGUCHI Koji, KATO Junji

Transactions of the Japan Society for Computational Engineering and Science Vol. 2023 ( 0 ) page： 20230001 - 20230001 2023.2

Authorship：Corresponding author Language：Japanese Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

The present study proposes a multi-material topology optimization method considering the strengths both of solid materials and interface. In order to consider multiple factors of Young’s modulus and strength at the same time, the DMO material interpolation function that the coefficients are given equivalently is applied. To resolve the singularity problem, we propose the stress definition adapted to the DMO material interpolation function. Furthermore, the graded interface with a two-step density filter is introduced to represent the interface on a density-based method. The tension/compression asymmetric interfacial strength criteria makes it possible to obtain an optimal layout in which the interface is not subjected to tensile strain. The validity of the method proposed in this study is verified with three structural models.

DOI： 10.11421/jsces.2023.20230001

HIGH-RESOLUTION MULTI-SCALE TOPOLOGY OPTIMIZATION USING FFT-BASED HOMOGENIZATION Reviewed

MATSUI Masayoshi, HOSHIBA Hiroya, OGURA Hiroki, KATO Junji

Japanese Journal of JSCE Vol. 79 ( 15 ) page： n/a 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers

Thanks to the development of additive manufacturing technology, it is becoming possible to produce materials with desired mechanical properties defined by their periodic microstructures. To design optimal microstructures, multi-scale topology optimization has been paid attention to in many engineering fields. However, its high computational cost prevents practical use, such as high-resolution 3D analysis for precision modeling and non-linear analysis assuming actual materials. In this study, to solve this problem, we focus on the homogenization approach using fast Fourier transform and develop a new optimization method with fast computing speed and low memory requirement. By performing stiffness maximization analyses with linear elastic materials, we demonstrate the validity and efficiency of the proposed method.

DOI： 10.2208/jscejj.22-15026

AN EXTENDED SIMP MODEL AND SENSITIVITY FORMULATION FOR TOPOLOGY OPTIMIZATION OF BRITTLE-DUCTILE COMPOSITE STRUCTURES Reviewed

FUJIWARA Mutsuki, HOSHIBA Hiroya, NISHIGUCHI Koji, KATO Junji

Japanese Journal of JSCE Vol. 79 ( 15 ) page： n/a 2023

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers

A structure with high strength and toughness is an ideal structure for engineering. Some existing composite structures demonstrate these performances with the proper combination of ductile and brittle materials. In this study, we propose a topology optimization method to maximize the strength and toughness of such composite structures by assuming a two-phase structure consisting of a brittle damage material for strength and a von-Mises elastoplastic material for toughness. It uses a unique material representation method, which partially combines two material constitutive laws with different mathematical structures. In this paper, a series of formulations of the method are described, and some numerical results are presented.

DOI： 10.2208/jscejj.22-15028

Design and evaluation of temporary brackets using topology optimization techniques Reviewed

Kitada Yukio, Kurokawa Takahiro, Nagasaki Ren, Matsumura Toshio, Nakamura Masaaki, Kato Junji

Journal of Structural Engineering, A Vol. 69A ( 0 ) page： 26 - 34 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers

The present paper aims at the development of temporary brackets used for erection of additional girders for bridge maintenance construction. A lightweight and highly rigid shape made of casting without welding joints is derived using topology optimization techniques. First, FEA (finite element analysis) of the current shape is performed, and topology analysis is performed using the result as a standard for comparison. After that, we use a three-dimensional sand mold additive manufacturing a test body, performance is evaluated through a full-scale loading test. From experimental results, the effectiveness of the optimal shape using the topology optimization technique is evaluated.

DOI： 10.11532/structcivil.69a.26

Large-Scale Topology Optimization for Unsteady Flow Using the Building-Cube Method Reviewed

Katsumata Ryohei, Nishiguchi Koji, Shimada Tokimasa, Hoshiba Hiroya, Kato Junji

Transactions of the Japan Society for Computational Engineering and Science Vol. 2023 ( 0 ) page： 20230007 - 20230007 2023

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

In recent years, topology optimization methods have been applied not only to structural problems but also to fluid flow problems. Most of the previous studies assume steady-state flow. In contrast, this paper focuses on topology optimization for unsteady flow, which is more general from an engineering point of view. However, unsteady flow topology optimization involves solving the governing and adjoint equations of a time-evolving system, which requires a huge computational cost for topology optimization with a fine mesh. Therefore, we propose a large-scale unsteady flow topology optimization based on the building-cube method (BCM), which is suitable for massively parallel computing. BCM is one of the hierarchical Cartesian mesh methods and is confirmed to have very good scalability. The governing equations are discretized by a cell-centered finite volume method based on the BCM. The objective sensitivity is obtained by the continuous adjoint method. Several numerical examples are demonstrated to discuss its applicability to large-scale computations.

DOI： 10.11421/jsces.2023.20230007

Multi-material topology optimization considering properties of solid materials and interface Reviewed

WATANABE Daiki, HOSHIBA Hiroya, NISHIGUCHI Koji, KATO Junji

Transactions of the Japan Society for Computational Engineering and Science Vol. 2022 ( 0 ) page： 20220017 - 20220017 2022.11

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

The present study proposes a multi-material topology optimization method considering the physical properties of solid materials and the interface. An extended two-step filtering technique is introduced to define material interface based on Helmholtz-type partial differential equations. Furthermore, the width of the interface region can be controlled based on this approach. To deal with the non-convexity of the problem caused by multi-material topology optimization, a material interpolation function in which the material volume fractions are mutually independent is used: this allows for the commutativity of constituent materials. The minimum mean compliance problem is considered in two different structural models. To solve this problem, sensitivities of the objective function and the constraint condition are derived. The usefulness of the proposed method is verified through several numerical examples.

DOI： 10.11421/jsces.2022.20220017

Study on two-phase material topology optimization for transient heat conduction Reviewed

TAKAARA Keisuke, HOSHIBA Hiroya, NISHIGUCHI Koji, KATO Junji

Transactions of the Japan Society for Computational Engineering and Science Vol. 2022 ( 0 ) page： 20220007 - 20220007 2022.8

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

In the field of topology optimization for heat conduction problems, the steady-state thermal conditions are usually assumed because of its theoretical ease of handling. However, for design problems such as casting dies and heat-dissipating parts, where not only the spatial distribution of temperature but also its temporal transition is important, a topology optimization method considering unsteady-state conditions is required. With this background, the present study deals with an unsteady-state heat conduction problem with a special objective function, namely minimizing temperature at the targeted time and space. The optimization problem is solved using a gradient-based optimization scheme and its accuracy of sensitivities with respect to design variables is investigated. Finally, the performance of the proposed method and a common problem for unsteady-state thermal problems are discussed through a series of the numerical examples.

DOI： 10.11421/jsces.2022.20220007

Two-scale topology optimization for transient heat analysis in porous material considering the size effect of microstructure

Naruethep Sukulthanasorn, Hiroya Hoshiba, Koji Nishiguchi, Mao Kurumatani, Robert Fleischhauer, Kuniharu Ushijima, Michael Kaliske, Kenjiro Terada, Junji Kato

Structural and Multidisciplinary Optimization Vol. 65 ( 7 ) 2022.7

Language：Japanese Publishing type：Research paper (scientific journal)

This paper presents a two-scale topology optimization framework for determining the optimal microstructure in porous material under transient heat conduction and transfer. The new optimization model, which can consider the surface area directly from microstructure topology as the size-dependent term, is introduced to enhance the heat transfer performance. In more detail, a homogenization method capable of considering the size-dependent microscopic heat transfer effect is adopted to express the microscopic material responses. A well-known material interpolation, referred to as the SIMP approach, and the design-dependent linear function are used for interpolating intermediate material properties. The minimal transient heat compliance is chosen as an objective function in this optimization problem. For the sensitivity analysis, a coupled-adjoint variable method is adopted to derive transient sensitivity formulation. The analysis shows that the proposed topology optimization model captures not only the transient heat but also the size effect of the microstructure in a transient heat analysis in porous material.

DOI： 10.1007/s00158-022-03257-2

Heat-transfer and pressure drop characteristics of micro-lattice materials fabricated by selective laser metal melting technology Reviewed International coauthorship

Takarazawa, S; Ushijima, K; Fleischhauer, R; Kato, J; Terada, K; Cantwell, WJ; Kaliske, M; Kagaya, S; Hasumoto, S

HEAT AND MASS TRANSFER Vol. 58 ( 1 ) page： 125 - 141 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Heat and Mass Transfer/Waerme- und Stoffuebertragung

This paper describes the findings of a numerical and experimental study on the heat transfer coefficient and pressure drop in micro-lattice blocks fabricated by selective laser metal melting and subjected to forced air convection. In particular, the influence of the unit-cell topology on the thermofluid performance of the lattice structure is examined in detail. In the present numerical study, five lattice block designs (BCC, BCCZ, FCC, FCCZ and F2BCC) are considered for investigation. Regarding effective thermal conductivity, the FCC and FCCZ lattices offer the best performance among the various lattices. In terms of heat transfer capacity per unit mass, the BCC and BCCZ lattices exhibit superior characteristics relative to the other lattices. Also, F2BCC lattice offers the lowest pressure loss for a given relative density. In addition, it is found that the heat transfer coefficients obtained by experiment lie between two numerical results having different strut diameter, which is due to the fact that the equivalent strut diameter in the as-manufactured samples is greater, due to the present of additional metal particles fused onto the surfaces of some struts. Moreover, it is found from our experimental investigation that the heat transfer coefficient h for the BCCZ is approximately 1.3 times higher than that for the BCC lattice for the same pressure loss.

DOI： 10.1007/s00231-021-03083-0

Transient thermal porous structure designed by two-scale concurrent topology optimization Reviewed

Naruethep Sukulthanasorn, Mao Kurumatani, Koji Nishiguchi, Junji Kato, Kenjiro Terada

Transactions of the Japan Society for Computational Engineering and Science Vol. 2022 ( 0 ) page： 20220004 - 20220004 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

The present paper proposes the novel design framework for thermal porous structure based on two-scale concurrent topology optimization subject to transient heat analysis. The optimization model considers the heat transfer through the microstructure surface to enhance the heat dissipation performance design. In particular, a well-known homogenization method incorporated the size-dependent term of microscopic heat transfer is exploited to obtain the material properties. Meanwhile, the unsteady-state heat condition is applied to the macrostructure. Furthermore, the heat compliance objective function and the derived analytical sensitivity formulations are adopted to determine the two-scale optimal topologies. As a numerical result, the concurrent design of micro-and macrostructures show the remarkable transient effect. It is also indicated that the microstructure size and the volume constraint are significant parameters for the design of heat performance.

DOI： 10.11421/jsces.2022.20220004

Large-scale Unsteady Flow Topology Optimization Using Building-cube Method

Katsumata Ryohei, Nishiguchi Koji, Shimada Tokimasa, Hoshiba Hiroya, Kato Junji

NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan Vol. 66 ( 0 ) page： 25 2022

Language：Japanese Publisher：National Committee for IUTAM

In recent years, topology optimization methods have been adopted not only for structural problems but also for fluid flow problems. Topology optimization for unsteady flows requires a fine mesh, especially for high Reynolds number flows, which is computationally expensive. Therefore, we propose an unsteady incompressible flow topology optimization method based on the building-cube method (BCM), which is suitable for massively parallel computing. The unsteady Navier-Stokes equations in the topology optimization procedure are solved by finite volume discretization, and the sensitivity of the objective function is obtained by continuous sensitivity analysis based on the adjoint variables method.

DOI： 10.11345/japannctam.66.0_25

Topology optimization for unsteady state thermal fluid problems

Takaara Keisuke, Hoshiba Hiroya, Takase Shinsuke, Nishiguchi Koji, Kato Junji

NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan Vol. 66 ( 0 ) page： 27 2022

Language：Japanese Publisher：National Committee for IUTAM

As regards thermal-fluid topology optimization research, only a few studies have considered the unsteady state thermal-fluid problem. In actual design problems, there are lots of cases in which temporal changes in temperature distribution are important rather than steady-state. In this study, the framework of a density-based topology optimization method for the unsteady thermal-fluid problem is proposed. The governing equations are unsteady-state incompressible Naiver-Stokes equation and thermal convection-diffusion equation, discretized with stabilized finite element method. The numerical analysis shows that the proposed framework captures the transient effect correctly and the results of optimization are physically reliable.

DOI： 10.11345/japannctam.66.0_27

Coupled simulation of fluid and visco-hyperelastic solid with Eulerian finite volume method

Nishiguchi Koji, Takeuchi Shusuke, Shimada Tokimasa, Katsumata Ryohei, Hoshiba Hiroya, Kato Junji

NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan Vol. 66 ( 0 ) page： 15 2022

Language：Japanese Publisher：National Committee for IUTAM

Unified Eulerian structure-fluid formulation is suitable for massively parallel simulation of complex-shaped material. However, it has not been applied to the simulation of viscoelastic material, which has many internal variables in conventional studies. Numerical simulations of viscoelastic material are essential for a wide range of engineering fields, such as a shock-absorbing structure. Considering the background above, we propose a unified Eulerian structure-fluid formulation with a visco-hyperelastic model in this study. The proposed method is verified by simulating the uniaxial tension test and shock-absorbing structure.

DOI： 10.11345/japannctam.66.0_15

Large-Scale Topology Optimization of Transient Incompressible Flow with Building-Cube Method

KATSUMATA Ryohei, NISHIGUCHI Koji, SHIMADA Tokimasa, HOSHIBA Hiroya, KATO Junji

The Proceedings of OPTIS Vol. 2022.14 ( 0 ) page： U00058 2022

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

In recent years, topology optimization methods have been adopted not only for structural problems but also for fluid flow problems. Topology optimization for unsteady flows requires a fine mesh, which is computationally expensive. Therefore, we propose an transient incompressible flow topology optimization method based on the building cube method (BCM), which is suitable for massively parallel computing. BCM is a type of hierarchical Cartesian mesh method that has been reported to have very good scalability. The transient Navier-Stokes equations in the topology optimization procedure are solved by a finite volume discretization based on the BCM. The sensitivity of the objective function is obtained by continuous sensitivity analysis based on the adjoint variables method.

DOI： 10.1299/jsmeoptis.2022.14.u00058

Multi-scale Topology Optimization Using FFT-based Homogenization with Elasto-plastic Material

MATSUI Masayoshi, HOSHIBA Hiroya, OGURA Hiroki, NISHIGUCHI Koji, KATO Junji

The Proceedings of OPTIS Vol. 2022.14 ( 0 ) page： U00052 2022

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

Thanks to the development of additive manufacturing technology, it is becoming possible to produce materials with desired mechanical properties defined by their periodic microstructures. Multi-scale topology optimization has been paid attention to in many engineering fields to design optimal microstructures. However, its high computational cost prevents practical use, such as high-resolution 3D analysis for precision modeling and non-linear analysis assuming actual materials. In this study, to solve this problem, we focus on the homogenization approach using fast Fourier transform and develop a new optimization method with fast computing speed and low memory requirement. By performing sample analyses, we demonstrate the validity and efficiency of the proposed method.

DOI： 10.1299/jsmeoptis.2022.14.u00052

Topology Optimization for Unsteady Coupled Thermal-Fluid Problems

TAKAARA Keisuke, HOSHIBA Hiroya, TAKASE Shinsuke, NISHIGUCHI Koji, KATO Junji

The Proceedings of OPTIS Vol. 2022.14 ( 0 ) page： U00045 2022

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

As regards thermal-fluid topology optimization problems, many beneficial results have been reported. However, only a few studies have considered the unsteady state thermal-fluid problem. In actual design problems, there are lots of cases in which temporal changes in temperature distribution are important rather than steady-state. In this study, the framework of a density-based topology optimization method for the unsteady thermal-fluid problem is proposed. The governing equations are unsteady-state incompressible Naiver-Stokes equation and thermal convection-diffusion equation, discretized with stabilized finite element method. The design sensitivity is computed accurately based on the adjoint variable method. The numerical analysis shows that the proposed framework captures the transient effect correctly and the results of optimization are physically reliable.

DOI： 10.1299/jsmeoptis.2022.14.u00045

A new constraint on principal stress direction variance to improve load bearing capacity

Kamada, H; Kato, J; Uozumi, H; Kikawa, K

STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION Vol. 64 ( 5 ) page： 3209 - 3225 2021.11

Language：Japanese Publisher：Structural and Multidisciplinary Optimization

The present study addresses a simplified topology optimization method to improve load bearing capacity. Topology optimization taking account of structurally nonlinear and complex behavior is an important topic from the viewpoint of mechanics. However, most methodologies require complex analytical derivation of sensitivity analysis and high computational cost to obtain the optimal solution. In light of this, we propose a practical design method employing the principal direction of Cauchy stress and the directional statistics, to improve load bearing capacity indirectly with much lower computational cost than those based on complex nonlinear structural analysis. Finally, we discuss setting of optimization problems, and demonstrate the accuracy and performance of the proposed method with a series of numerical examples.

DOI： 10.1007/s00158-021-03079-8

Robust topology optimization based on finite strain considering uncertain loading conditions

Nishino, T; Kato, J

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Vol. 122 ( 6 ) page： 1427 - 1455 2021.3

Language：Japanese Publisher：International Journal for Numerical Methods in Engineering

The present study proposes a method of robust topology optimization assuming uncertainties in the magnitude and direction of loads applied to a geometrically nonlinear structure. The objective function is the sum of the expected value and the standard deviation of end-compliance of a structure with a compressible Neo-Hookean hyperelasticity. In this study, quadratic approximation of the end-compliance with respect to random variables is employed to reduce computational cost. To ensure its accuracy, a complete analytical formulation is derived, and the performance and limitation of the proposed method are deeply discussed. The performance of the proposed method is verified and its numerical examples emphasize the importance of considering geometrical nonlinearity to obtain robust structures with respect to uncertainties of loading conditions. Finally, we have obtained a finding that the optimized network system consisting of thin members plays a significant role in the improvement of robustness of structures.

DOI： 10.1002/nme.6584

Implicit Eulerian fluid-structure interaction method considering interfacial discontinuity of velocity field

NISHIGUCHI Koji, SHIMADA Tokimasa, HOSHIBA Hiroya, Kato Junji

The Proceedings of The Computational Mechanics Conference Vol. 2021.34 ( 0 ) page： 228 2021

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

We propose an implicit Eulerian finite volume formulation using the reference map technique and Lagrangian maker particles to simulate deformable solid-fluid interaction problems. In this numerical framework, a set of Lagrangian maker particles represent the solid region and carry the initial position vector of solid (i.e., reference map), whereas basic equations and spatial derivatives are computed on the spatially fixed mesh. We will demonstrate several numerical examples in the presentation to validate the present approach.

DOI： 10.1299/jsmecmd.2021.34.228

A new constraint of variance of principal stress direction for improving structural strength in Topology optimization Reviewed

KAMADA Hiroki, KATO Junji, KYOYA Takashi

Transactions of the Japan Society for Computational Engineering and Science Vol. 2020 ( 0 ) page： 20200006 - 20200006 2020.4

Language：Japanese Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

The present study proposes a simplified topology optimization method to improve structural strength. Topology optimization considering structurally nonlinear behavior is one of the important topics. However, most of those methodologies request the complicated analytical derivation of sensitivity analysis and also high computational costs to obtain the optimal solution. This is the reason why the optimal design method based on linear structural analysis is still common approach in practice. However, optimal layouts based on linear structural analysis may lose the structural stability under larger or uncertain load.From this background, we propose a method of practical and simplified topology optimization to improve structural buckling behavior with much lower computational costs than that of optimal design based on complicated nonlinear structural analysis. Finally, we discuss the setting of the optimization problem improving the structural strength and demonstrate the accuracy and performance of the proposed method by a series of numerical examples.

DOI： 10.11421/jsces.2020.20200006

Microscopic design and optimization of hydrodynamically lubricated dissipative interfaces Reviewed

Finite thermo-elastic decoupled two-scale analysis Reviewed Open Access

Robert Fleischhauer,Tom Thomas, Junji Kato, Kenjiro Terada, Michael Kaliske

International Journal for Numerical Methods in Engineering Vol. 121 ( 3 ) page： 355 - 392 2020.2

数理的均質化法に基づく材料微視構造のトポロジー最適（特集：モルフォロジクス：形がつくる新しいセラミックスと機能）

加藤準治

日本セラミックス協会誌 ( 55 ) page： 377-382 2020

弾塑性挙動を考慮したトポロジー最適化における解析的感度導出法とその後の展開

加藤準治

計算工学 Vol. 25 ( 1 ) page： 3-7 2020

数理的均質化法に基づく材料微視構造のトポロジー最適

加藤準治

日本セラミックス協会誌 Vol. 55 page： 377 - 382 2020

B.A. Cakal, İ. Temizer, J. Kato, K. Terada

International Journal of Numerical Methods for Engineering Vol. 120 ( 2 ) page： 153 - 178 2019.10

Study on Optimal Design for Sandwich Beams Based on the Ground Structure Method Reviewed

KOIKE Yusuke, USHIJIMA Kuniharu, KATO Junji

Transactions of the Japan Society for Computational Engineering and Science Vol. 2019 ( 0 ) page： 20190006 - 20190006 2019.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

In this study, an optimal design of lattice sandwich panels based on the ground structure method has been investigated. In our calculation, the sandwich panels were assumed to be subjected to three-point bending load. The lattices discussed in this paper can be manufactured by using the selective laser metal melting machine. Based on the former experimental study on the manufacturable diameter of each strand, a new equation for controlling the cross-section of each strand was introduced, which is based on the multiphase material optimization approach. In this paper, three kinds of unit-cell models (BCC, f2BCC and half-BCC) were applied as an initial shape, and the effect of the micro-architecture on the optimized result was discussed. It is found that the lattice composed of f2BCC unit behaves the lowest compliance among three geometries. The optimized shape was manufactured with a good accuracy by SLM.

DOI： 10.11421/jsces.2019.20190006

Topology optimization with geometrical nonlinearity considering uncertain loading condition Reviewed

NISHINO Takayuki, KATO Junji, KYOYA Takashi

Transactions of the Japan Society for Computational Engineering and Science Vol. 2019 ( 0 ) page： 20190004 - 20190004 2019.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

The present study proposes a topology optimization method considering finite deformation for loading uncertainty. The loading angle is assumed to be uncertain as a condition. The objective is to minimize expectation and standard deviation of end-compliance obtained by means of a Total Lagrangian finite element formulation. In this case, an analytical estimation of the expectation and the standard deviation is not allowed. In order to solve this problem, we approximate the end-compliance by a Taylor series expansion and derive the mathematical formulation. In this approach, the second derivative of the objective function is necessary to keep the accuracy in sensitivity. This phenomenon is investigated in terms of numerical validations. Finally, some numerical examples demonstrate the usefulness of the proposed method.

DOI： 10.11421/jsces.2019.20190004

STRESS-CONSTRAINED TOPOLOGY OPTIMIZATION OF INFILL STRUCTURE

KAMADA Hiroki, HOSHIBA Hiroya, KATO Junji, KYOYA Takashi

Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)) Vol. 75 ( 1 ) page： 68 - 85 2019

Language：Japanese Publisher：Japan Society of Civil Engineers

Recent development of Additive Manufacturing technology made it possible to manufacture the complex-shaped porous structures: this leads to further development and research for porous structures with special functions and characteristics. In particular, the so-called infill structure is paid attention for its high strength and robustness, and also the optimal design methods for infill structures have been reported. However, few studies has examined to extend to the practical design with stress constraint. With this reason, the present study addresses a topology optimization method for infill structures to avoid stress concentration by adding the local volume constraint and p-norm type stress constraint concept. In addition, we propose a new method, namely variable influence radius, to solve a specific problem which arises in infill optimization. Finally we discuss the setting of optimization problem and demonstrate the accuracy and performance of the proposed method by a series of numerical examples.

DOI： 10.2208/jscejam.75.68

OPTIMAL DESIGN OF LATTICE STRUCTURE CONSIDERING CONSTRAINTS THROUGH ADDITIVE MANUFACTURING PROCESS

Koike, Y; Ushijima, K; Kato, J

SECOND INTERNATIONAL CONFERENCE ON SIMULATION FOR ADDITIVE MANUFACTURING (SIM-AM 2019) page： 205 - 214 2019

Optimal design of lattice structure considering constraints through additive manufacturing process Open Access

Koike Y., Ushijima K., Kato J.

2nd International Conference on Simulation for Additive Manufacturing, Sim-AM 2019 page： 205 - 214 2019

Publisher：2nd International Conference on Simulation for Additive Manufacturing, Sim-AM 2019

In this research, an optimization design of the lattice structure is investigated, which is based on the ground structure method. In recent years, as a result of rapid development of additional manufacturing technology, it has become possible to manufacture complicated shapes including periodic lattice structure. However, in real metal lattice samples, geometric imperfections may exist in every unit because of the stochastic influence of feasible processing path. In this study, a new ground structure method which does not leave elements with small cross sectional area was proposed. In particular, the effect of geometric constraints caused by additive manufacturing techniques on optimized results are discussed based on the robust topology optimization combining perturbation methods for quantifying uncertainty. In the end, a robust topology optimization was also discussed as a problem to minimize expected value and standard deviation of compliance.

Multi-scale topology optimization considering elastoplastic composite material Reviewed

Hoshiba Hiroya, OGAWA Shun, KATO Junji, KYOYA Takashi

Transactions of the Japan Society for Computational Engineering and Science Vol. 2018 ( 0 ) page： 20180015 - 20180015 2018.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JAPAN SOCIETY FOR COMPUTATIONAL ENGINEERING AND SCIENCE

The present study proposes topology optimization of microstructure considering elastoplastic deformation based on a decoupling multi-scale analysis. Energy absorption capacity of macrostructure is maximized under a prescribed material volume of microstructure. It is assumed that microstructure consists of a two-phase material based on elastoplastic von Mises model and that macrostructure is modeled with anisotropic Hill’s elastoplasticity. In this study, we extend the analytical sensitivity method used for mono-scale analysis to the decoupling multi-scale analysis and propose a framework of new multi-scale topology optimization, which can reduce the computational costs with keeping sensitivities highly accurate. It is verified by a series of numerical examples that the proposed method provides reliable optimization results and has a great potential for advanced material design.

DOI： 10.11421/jsces.2018.20180015

Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16J02523/

Stability evaluation of a tunnel in swelling ground by a simplified multi-scale analysis using a secant stiffness Reviewed

Xiaodong LIU, Hitoshi UNOSAWA, Junji KATO, Takashi KYOYA

2018.10

Current and future trends in topology optimization for additive manufacturing Reviewed

Jikai Liu, Andrew T. Gaynor, Shikui Chen, Zhan Kang, Krishnan Suresh, Akihiro Takezawa, Lei Li, Junji Kato, Jinyuan Tang, Charlie C. L. Wang, Lin Cheng, Xuan Liang, Albert. C. To

Structural and Multidisciplinary Optimization Vol. 57 ( 6 ) page： 2457 - 2483 2018.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Verlag

Manufacturing-oriented topology optimization has been extensively studied the past two decades, in particular for the conventional manufacturing methods, for example, machining and injection molding or casting. Both design and manufacturing engineers have benefited from these efforts because of the close-to-optimal and friendly-to-manufacture design solutions. Recently, additive manufacturing (AM) has received significant attention from both academia and industry. AM is characterized by producing geometrically complex components layer-by-layer, and greatly reduces the geometric complexity restrictions imposed on topology optimization by conventional manufacturing. In other words, AM can make near-full use of the freeform structural evolution of topology optimization. Even so, new rules and restrictions emerge due to the diverse and intricate AM processes, which should be carefully addressed when developing the AM-specific topology optimization algorithms. Therefore, the motivation of this perspective paper is to summarize the state-of-art topology optimization methods for a variety of AM topics. At the same time, this paper also expresses the authors’ perspectives on the challenges and opportunities in these topics. The hope is to inspire both researchers and engineers to meet these challenges with innovative solutions.

DOI： 10.1007/s00158-018-1994-3

Multi-phase field topology optimization of polycrystalline microstructure for maximizing heat conductivity Reviewed

Junji Kato, Shun Ogawa, Toshiki Ichibangase, Tomohiro Takaki

Structural and Multidisciplinary Optimization Vol. 57 ( 5 ) page： 1937 - 1954 2018.5

Publishing type：Research paper (scientific journal)

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. The present study proposes multi-scale topology optimization for polycrystalline microstructures applying a multi-phase field method. The objective function is to maximize the heat compliance of macrostructure and the equality constraint is the material volume of constituents in an alloy consisting of two components with different heat conductivity. Two-scale steady-state heat conduction problem based on a homogenization method is conducted. The Allen-Cahn non-conserved time evolution equation with the additional volume constraint scheme is employed as the optimization strategy for updating the crystal configuration. In the time evolution equation, sensitivities of objective function with respect to phase-field variables are considered to relate topology optimization to the multi-phase field method. It is verified from a series of numerical examples that the proposed method has great potential for the development of material design underlying polycrystalline structure.

DOI： 10.1007/s00158-018-1965-8

Two-scale topology optimization for composite plates with in-plane periodicity Reviewed

Shinnosuke Nishi, Kenjiro Terada, Junji Kato, Shinji Nishiwaki, Kazuhiro Izui

International Journal for Numerical Methods in Engineering Vol. 113 ( 8 ) page： 1164 - 1188 2018.2

Language：English Publishing type：Research paper (international conference proceedings) Publisher：John Wiley and Sons Ltd

This study proposes a two-scale topology optimization method for a microstructure (an in-plane unit cell) that maximizes the macroscopic mechanical performance of composite plates. The proposed method is based on the in-plane homogenization method for a composite plate model in which the macrostructure is modeled using thick plate theory and the microstructures are three-dimensional solids. Macroscopic plate characteristics such as homogenized plate stiffnesses and generalized thermal strains are evaluated through the application of numerical plate tests applied to an in-plane unit cell. To handle large rotations of the composite plates, we employ a co-rotational formulation that facilitates working with the two-scale plate model formulated within a small strain framework. Two types of objective functions are tested in the presented optimization problems: one minimizes the macroscopic end compliance to maximize the macroscopic plate stiffness, whereas the other maximizes components of a macroscopic nodal displacement vector. Analytical sensitivities are derived based on in-plane homogenization formulae so that a gradient-based method can be employed to update the topology of in-plane unit cells. Several numerical examples are presented to demonstrate the proposed method's capability related to the design of optimal in-plane unit cells of composite plates. Copyright © 2017 John Wiley &amp
Sons, Ltd.

DOI： 10.1002/nme.5545

Micro-macro concurrent topology optimization for nonlinear solids with a decoupling multiscale analysis Reviewed

Junji Kato, Daishun Yachi, Takashi Kyoya, Kenjiro Terada

International Journal for Numerical Methods in Engineering Vol. 113 ( 8 ) page： 1189 - 1213 2018.2

Language：English Publishing type：Research paper (international conference proceedings) Publisher：John Wiley and Sons Ltd

The present study proposes a method of micro-macro concurrent topology optimization for a two-phase nonlinear solid to minimize the end compliance of its macrostructure undergoing large deformation. To reduce the computational costs to solve a 2-scale boundary value problem under geometrically nonlinear setting, we use the so-called method of decoupling multiscale structural analysis, in which the microscopic and macroscopic boundary value problems are decoupled in the homogenization process. An isotropic hyperelasticity model is used for the constitutive model for microstructures, while an orthotropic one is assumed to represent the macroscopic material behavior. Owing to this decoupling framework, the micro-macro concurrent optimization problem can be split into 2 individual problems at the microscale and macroscale for the sake of algorithmic simplicity. Also, a 2-scale adjoint sensitivity analysis can be performed within the framework of computational homogenization. It is verified from a series numerical examples that the proposed method is capable of computing the optimal structures at both microscale and macroscale, according to the level of applied load.

DOI： 10.1002/nme.5571

Verification of optimization scheme for infill structure considering elastoplastic deformation

Kamada Hiroki, Hoshiba Hiroya, Kato Junji, Kyoya Takashi

The Proceedings of OPTIS Vol. 2018.13 ( 0 ) page： 113 2018

Topology optimization for porous filling structure

KAMADA Hiroki, HOSHIBA Hiroya, KATO Junji, KYOHYA Takashi

The Proceedings of The Computational Mechanics Conference Vol. 2018.31 ( 0 ) page： 312 2018

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

Infill structure - which consists of porous and solid phases over the structures, is getting a lot of attention due to its multi-functional performance, such as light weight, high-thermal convention and the potential redundancy. Nowadays, the manufacturing for this kind of geometrically complicated structure becomes possible by the recent development of Additive Manufacturing technology and furthermore topology optimization is often applied for the design to improve those structural performances. In infill topology optimization, too slender members often remain as a result of the severe density local constraints: this leads to undesirable local failure in the members even under small deformation. In this research, we propose a filtering method to avoid those thin members and local failure by introducing a variable length radius.

DOI： 10.1299/jsmecmd.2018.31.312

Topology optimization considering geometrical nonlinearity under uncertain loading condition

NISHINO Takayuki, HOSHIBA Hiroya, KATO Junji, KYOYA Takashi

The Proceedings of The Computational Mechanics Conference Vol. 2018.31 ( 0 ) page： 277 2018

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

The present paper proposes a topology optimization method considering finite deformation for loading uncertainty. The loading angle is assumed to be uncertain as a condition. The objective is to minimize mean and standard deviation of structural compliance. In case of finite deformation theory, an analytical estimation of the mean and the standard deviation is not allowed. In order to solve this problem, we approximate the objective function by a Taylor series expansion and derive the mathematical formulation. In this approach, the second derivative of the objective function is necessary to keep the accuracy in sensitivity. This phenomenon is investigated in terms of numerical validations. Finally, some numerical examples demonstrate the usefulness of the proposed method.

DOI： 10.1299/jsmecmd.2018.31.277

Optimal Design of Lattice Structure Considering Constraints via Additive Manufacturing

KOIKE Yusuke, USHIJIMA Kuniharu, KATO Junji

The Proceedings of The Computational Mechanics Conference Vol. 2018.31 ( 0 ) page： 134 2018

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

In this research, an optimization design of the lattice structure is investigated, which is based on the ground structure method. In recent years, as a result of the rapid development of additional manufacturing technology, it has become possible to manufacture complicated shapes including periodic lattice structure. However, in real metal lattice samples, geometric imperfections, such as irregularities and geometric constraints on the surface of the beam elements, i.e. the maximum overhang angles exist in every unit because of the stochastic influence of feasible processing path. So in this study, a lattice structure was targeted as the shape before optimization, and a new ground structure method which does not leave elements with small cross sectional area was proposed. Here, the lattice structure studied in this paper can be manufactured by the selective laser melting machine. In addition, the effect of geometric constraints caused by AM manufacturing techniques on optimized results are discussed based on robust topology optimization combining perturbation methods for quantifying uncertainty. In the end, a robust topology optimization was discussed as a problem to minimize expected value and standard deviation of compliance.

DOI： 10.1299/jsmecmd.2018.31.134

Topology Optimization for Vibration Suppression

ENDO Takuma, HOSHIBA Hiroya, KATO Junji, KYOYA Takashi

The Proceedings of The Computational Mechanics Conference Vol. 2018.31 ( 0 ) page： 291 2018

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

This study deals with the ideal topological design of vibrating structures. For static structures, well-known compliance minimization is defined as the inner product of the external force and static displacement. However, for dynamic structures with time-varying forces and displacements, defining a measure for dynamic stiffness are required. Therefore, various objective functions have been proposed to suppress the response of vibrating structures. In this study, these various objective functions are compared from the viewpoint of vibration suppression. The examples of numerical calculation when adopting mean strain energy and mean squared dynamic compliance as objective functions are presented.

DOI： 10.1299/jsmecmd.2018.31.291

Micro-texture design and optimization in hydrodynamic lubrication via two-scale analysis Reviewed

A. Waseem, I. Temizer, J. Kato, K. Terada

STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION Vol. 56 ( 2 ) page： 227 - 248 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

A novel computational surface engineering framework is developed to design micro-textures which can optimize the macroscopic response of hydrodynamically lubricated interfaces. All macroscopic objectives are formulated and analyzed within a homogenization-based two-scale setting and the micro-texture design is achieved through topology optimization schemes. Two non-standard aspects of this multiscale optimization problem, namely the temporal and spatial variations in the homogenized response of the micro-texture, are individually addressed. Extensive numerical investigations demonstrate the ability of the framework to deliver optimal micro-texture designs as well as the influence of major problem parameters.

DOI： 10.1007/s00158-017-1713-5

Phase-field topology optimization model that removes the curvature effects Reviewed

Tomohiro Takaki, Junji Kato

Mechanical Engineering Journal 2017.4

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

The conventional phase-field topology optimization (PFTO) models minimize not only the objective function but also the interface energy. In the present study, a new PFTO model, which minimizes only the objective function, is developed by removing the curvature effect from the conventional PFTO model. Simulations of elastic strain energy minimization under a constant-volume constraint condition of a cantilever are performed using the developed and conventional PFTO models. From the simulation results, we confirm that the developed PFTO model that removes the curvature effects can efficiently optimize only the objective function.

DOI： 10.1299/mej.16-00462

Multiscale stability analysis of a tunnel in swelling rockmass applying secant stiffness

Xiaodong Liu, Junji Kato, Takashi Kyoya

4th ISRM Young Scholars Symposium on Rock Mechanics, YSS 2017 Vol. 2017-May page： 284 - 287 2017

Publishing type：Research paper (international conference proceedings)

Damage of tunnels often occurs in Japan caused by swelling smectite rockmass. For an effective countermeasure against the damage, mechanical interaction between tunnel lining and swelling rock mass are analyzed by a two-scale analysis based on a homogenization theory in this study. In the microscopic scale, swelling of smectite minerals and damage process of surrounding intact rocks induced by the swelling of smectite minerals are analyzed by a 3D continuous damage model. This microscopic analysis provides the averaged volumetric change and the damaged macroscopic stiffness of the representative volumetric element (RVE) of rock mass. In the macroscopic scale, therefore, stress distribution within/around the tunnel lining can be reasonably analyzed by using the averaged secant stiffness and its volumetric strain of the RVE. The mechanical interaction between the tunnel lining and swelling rock mass is discussed and examined as some case studies are carried out.